For fans, Leon Russell’s induction into the Rock and Roll Hall of Fame had always been a question of when, not if. The Oklahoma-born singer and piano player, who was inducted in 2011, has enjoyed a long career playing rock ’n’ roll, blues and gospel, both on his own and accompanying some of popular music’s leading lights. As a session musician, he has accompanied everyone from Doris Day, Frank Sinatra and Glen Campbell to Jerry Lee Lewis, Bob Dylan and The Rolling Stones. Russell’s “Delta Lady” was a 1969 hit for British bluesman Joe Cocker, and Russell was the organizer of Cocker’s 1970 Mad Dogs and Englishmen tour, and a performer at George Harrison’s Concert for Bangladesh in 1971. Though Russell has slowed down considerably over the last decade, he returned to the spotlight with the release of The Union, a 2010 double-album he recorded with fellow keyboard artist Elton John.